Mime import with attachments/mbx import

[PureMoxie]

When dragging a mime message into UR, the attachments are indexed. I think it would be nice if the attachments were decoded on import and added as child items of the message; if this could be done, I think having the keywords associated with the attachments instead of the message would make sense.

Also, it would be great if an import for generic mbx style mailboxes were added, since quite a few mailers use this format.